Alkylation refers generally to the addition of an alkyl group to an organic compound. One well-known alkylating agent useful in the preparation of a wide variety of alkylated derivatives is the olefin. For example, dodecylbenzene, a useful precursor for the surfactant industry may be prepared by the alkylation of benzene with dodecene in the presence of an aluminum chloride catalyst. The aluminum chloride catalyst continuously deactivates and forms a sludge which is recovered and regenerated only at great cost and difficulty. In all of these processes a solid catalyst which is easily separated from the reaction mixture is desirable.
Other examples of commercially important alkylation processes include the alkylation of benzene with ethylene to yield ethylbenzene, which may be subsequently converted to styrene; and the alkylation of benzene with propylene to yield cumene, which may be subsequently converted to phenol and acetone, respectively. Catalysts useful in these processes include phosphoric acid supported on kieselguhr and aluminum chloride. In each of the above benzene alkylation processes the tendency to form polyalkylated derivatives, as impurities, is a noted problem.
In U.S. Pat. Nos. 3,037,052; 3,107,441; and 3,239,575, the use of various forms of sulfonated polystyrene as a catalyst for alkylation processes is disclosed. The difficulties of using sulfonated polystyrene include (1) cleaning residual organic "tars" from the catalyst; (2) gradual changes in the catalyst properties due to the alkylation of unsulfonated styrene residues; and (3) physical fragility of highly sulfonated styrene-divinyl benzene copolymers. In these patents, there is no mention of the use of polyfluorosulfonic acid polymers as catalysts for the alkylation processes described herein. Thus, in U.S. Pat. No. 3,239,575 it is proposed to alkylate aromatic hydrocarbons using as a catalyst a sulfonated synthetic resin copolymer of a vinyl aromatic compound and a divinyl cross-linking agent, having less than 4 wt. % cross-linking, it being said that such resins having more than 4% cross-linking, as in conventional sulfonated polystyrene resins, have no activity for alkylation of benzene with polylene. However, such lower cross-linked polymers have disadvantageous properties of compressability, poorer strength, etc. In contrast, my fluorocarbon polymer sulfonic acids do not have these problems.
Kapura and Gates report in an article "Sulfonated Polymers as Alkylation Catalysts", Industrial Engineering Chemistry Product Research Development, Vol. 12, No. 1, pp. 62-66 (1973), on tests of several sulfonated polymers for activity as alkylation catalysts. All of the experiments by these authors were carried out in vapor phase and they found that the catalysts rapidly desulfonated and formed coke. No alkylation products were obtained from a feed of isobutane and propylene in a mole ration of about 5/1 with a sulfonated fluorocarbon vinyl ether polymer at 260.degree. C. In aromatic alkylation the other sulfonated polymers lost acidity; the acidity loss could not be measured for the fluorocarbon polymer because the catalyst partially fused. The authors concluded that "none of the sulfonated polymers will be a practically useful catalyst at temperatures greater than about 150.degree. C.". Regardless of Kapura et al's speculation, without data about liquid phase aromatic alkylation with sulfonated polymers generally, their vapor phase data, even at the lower temperature, indicates the opposite: None of the sulfonated polymers tried by Kapura et al would be expected to be effective as commercial alkylation catalysts. The present invention is a liquid phase aromatic alkylation process with fluorocarbon polymer sulfonic acid catalyst and is based upon the finding that substantially higher selectivities are obtained than reported by Kapura and Gates.